Paradigms such as time-intensity trades have often been used to identify the longest period over which the ear can integrate (or summate) auditory information. This proposal will study instead the minimum time over which the ear must summate auditory information. We call this the minimum integration time. This can be measured by using a short signal such as a click surrounded by a masker such as noise. Clearly the observer should integrate for no longer than the signal duration and will do so unless the signal duration is shorter than the minimum integration time. Thus we can determine this minimum temporal parameter by varying the duration of the noise surrounding the click. When the noise becomes shorter than the minimum integration time, detection should improve. If the noise is longer than the minimum integration time, the signal-to-noise ratio should be constant and detection should, therefore, remain constant. The break point in this experimental function we call the critical masking interval. This experiment will be recognized as a temporal analog of Fletcher's critical band experiment. We propose to study the critical masking interval as a function of frequency in three paradigms which are temporal analogs of critical band studies: these are (1) Fletcher's critical band study, (2) Greenwood's masking paradigm, (3) Zwicker's masking paradigm. In these three experiments the masking interval will be determined for signals which are increments. In two additional experiments the interval is determined for signals which are decrements: these are the (1) detection of a silent interval placed in the temporal center of a noise burst and (2) detection of a silent interval placed in the temporal center of two tone bursts shaped by a Hamming window. We also determine the dependency of the critical masking interval on signal duration, on masker level, and we measure the interval in a dichotic masking experiment. Finally, we apply the notion of a temporal integrator to the perception of offset of a stimulus and to nonadditivity of masking.